Red-green colour blindness test, free

Test for red-green colour blindness: free colour vision test online

Six colour plates, each with a number in it. Someone with a red-green deficiency does not see some of them, or reads a different number. The test takes about two minutes, needs no signup and stores nothing. It is an indication, not a diagnosis: that needs an eye specialist with calibrated plates.

Set your screen to a normal brightness, sit at your usual distance, and turn off blue light filters, night mode and colour filters for the duration of the test. Those filters shift exactly the colours this test depends on.

What is a red-green deficiency?

The eye has three cone types, for short, medium and long wavelengths. In a red-green deficiency one of the two cones for red and green is missing or shifted in its sensitivity. The person does not see worse; they sort certain pairs of colours differently [3].

Protanomaly

The long-wavelength cone is shifted. Red looks darker and less saturated, and red and green move closer together. This is anomalous trichromacy: three cone types work, one of them differently.

Deuteranomaly

The same for the medium-wavelength cone. The most common form of all, and often so mild that a test is what reveals it.

Protanopia

The long-wavelength cone is absent. Red, orange, yellow and green collapse onto one axis, and red also looks noticeably dark.

Deuteranopia

The medium-wavelength cone is absent. As with protanopia two cone types remain, but the brightness of red stays close to normal.

In everyday speech all of this is called red-green colour blindness. Medically that only fits the second group, protanopia and deuteranopia, where a cone type really is missing. Complete colour blindness, where someone sees no colour at all, is something else and is very rare.

How common is red-green colour blindness?

About 8 percent of men and about 0.4 percent of women of European descent have a red-green deficiency [1]. The National Eye Institute gives the same order of magnitude, around one in twelve men [2]. The cause sits on the X chromosome, which is why men are affected far more often than women.

Among men of Chinese and Japanese ethnicity the share is lower than in Europe, between 4 and 6.5 percent [1].

Deuteranomaly is the single most common form. It is often mild enough that a test is what reveals it.

The deficiency is inherited and does not change over a lifetime. If your colour vision changes suddenly, that is a reason to see an eye doctor promptly.

Side by side: the same plate with a simulated deficiency

On the left the plate as normal colour vision sees it. Beside it the same plate converted to the colour perception of deuteranopia and of protanopia. The conversion follows the method of Vienot, Brettel and Mollon [4]. A simulation shows which differences disappear; it is not a picture of how someone experiences the world.

Colour plate in green and red tones, as it appears without a deficiency. — Normal colour vision

The same colour plate converted to Simulation: deuteranopia. The dots differ only in yellow and grey tones. — Simulation: deuteranopia

The same colour plate converted to Simulation: protanopia. The dots differ only in yellow and grey tones. — Simulation: protanopia

What this test cannot do

The limits of this test:

Your screen is not calibrated. Panel, brightness, colour profile, night mode and ambient light all shift the colours of the plates.

The test does not separate protan from deutan. That needs plates for both axes, or an anomaloscope.

It does not measure severity. A mild anomaly can pass every plate.

Six plates are few. Clinical test books use many more, including plates designed to tell the forms apart.

A result from this page is not evidence. For a driving licence, an application or training, only a specialist examination counts.

This is your website for 8 percent of your male visitors

The same perception the plates rely on decides whether your website works. When information is carried by colour alone, part of your audience never receives it.

Required fields marked only in red

A red outline with no text beside it says nothing to part of your visitors. Success Criterion 1.4.1 Use of Color (Level A) requires that colour is not the only means [5].

Charts with a colour legend

Red and green lines with no labels, patterns or symbols are exactly the case the plates above imitate.

Status as a traffic light

Green dot means fine, red dot means error: without a word or a symbol the meaning stays open.

Text that is too faint

Regardless of colour vision, 1.4.3 Contrast (Minimum) asks for at least 4.5:1 for normal text [6], and 1.4.11 asks for 3:1 for user interface components and meaningful graphics [7].

Our free check tests your page for contrast failures under 1.4.3 among other things, and for patterns that carry information by colour alone. It does not find everything: whether colour is the only carrier of a meaning can only partly be decided automatically, and the rest belongs in a manual review.